Asynchronous programming

[Terry Reedy]

On 8/11/2016 2:34 AM, Christian Gollwitzer wrote:
> Am 11.08.16 um 06:38 schrieb Terry Reedy:
>> You might be able to glean something from the succession of files I
>> uploaded to
>> https://bugs.python.org/issue27546
>> Integrate tkinter and asyncio (and async)
>>
>> I started with just mixing tk and asyncio callbacks.  After some
>> struggle with similar question as you ask above, I ended up with more or
>> less callback free code using async def and async for. Once I got over
>> the hump, I rather like it.

My next experiment, not uploaded, is adapting tk mainloop so it can be 
used instead of asyncio.loop.runforever as the driver for async def and 
async for and await.  There is either a simple bug I overlooked or I am 
missing some detail of how the future and task interact.

> Interesting discussion! Tcl itself acquired coroutines some years ago
> (in 8.6) and people in this community are very excited with async based
> programming.

When I read something like "Python finally acquired an event loop in 
3.4" I wonder where people have been.  The tk event loop has been in 
Python perhaps for 2 decades, and one actually could call select every 
xx milleseconds.  The main problem is that tcl/tk does not do file 
events on Windows.  The asyncio people did tackle that, but ended up 
with two loops, Selector and Proactor, neither of which are as complete 
as Selector on *nix.  Tcl/tk could try to borrow than work.

> I'm convinced that it is possible to integrate Tcl's event loop with
> asyncio's loop without regular update polling. This might require a
> patch to Tkinter at the C level. For example, an easy way is to put
> Tcl/Tk in it's own thread. The Tcl event loop can be woken up from a
> different thread by the TclThreadQueueEvent() and TclTheradAlert() API
> calls. Basically, you would spawn a new thread (from the C level), when
> loading Tkinter, which loads Tk and sits in a Tcl event loop ("vwait
> forever"). tk.eval() and tk.call() would be redefined to post events
> using the aforementioned functions. When a Tcl callback arrives, it
> would send an event to asyncio in the main thread - no idea how this
> works, though. In the end, it would also allow to use Tkinter from
> different Python threads, because all calls would be rooted to the one
> instance only.

-- 
Terry Jan Reedy